It is the goal of this grant to contribute to an understanding of the molecular basis of cell-mediated immune response. The major focus will be on products of activated lymphocytes (PALs), and particularly those produced by activated T-lymphocytes, such as migration inhibitory factor (MIF), cell cooperation factor and interferon. In order to study and distinguish the various factors, double labeling techniques utilizing H3 and C14 amino acids will be employed, and the nature of "ratiolabeled" proteins, i.e. proteins synthesized either de novo or in increased amounts in antigen-stimulated relative to control cultures, will be studied. PALs will be characterized on the basis of size (Kd on Sephadex), charge (pI on isoelectric focusing) and label incorporation (H3/C14 ratio). Long term lymphoid cell lines will be screened for the production of certain PALs identical to those produced by antigen-sensitive T-lymphocytes. The mechanism of action of PALs in three separate systems will be considered in detail. First, the mode of action of MIF on macrophage surface enzymes, and on the differentiation of macrophage precursors into mature macrophages will be explored. The nature of the PALs produced by T-cells which facilitates PFC production by B-lymphocytes will be studied. Additionally, the relationship of PALs to T-lymphocyte-target cell cytotoxicity will be explored using isotopic label as a marker for PALs. By understanding the nature and function of PALs it is hoped that a clear understanding of regulation and activation of T-cells may be achieved, and that useful quantitative radiochemical assays for products of activated human lymphocytes may be developed.